1. Field of the Invention
This invention relates to an air bag for an air bag device that is to be mounted in a vehicle and more particularly to an air bag for protecting a seat occupant in the case of collision or the like and to a folding method therefor.
2. Description of the Related Art
The air bag device is required to be compact such that it is preferably mounted in a vehicle and that it does not occupy a large space. Furthermore, various contrivances are carried out for more preferable deployment characteristics and, for example, for making it have a deployment characteristic that is directed obliquely downwardly. Due to them, there were a tendency toward the increase of the folding operation steps and a tendency toward the increase in difficulty for an operator since the operation steps themselves are complicated.
Furthermore, there is a contrivance to obtain preferable deployment characteristics to a seat occupant having a different seating posture by adding parts such as tether belt, for the above-mentioned more preferable deployment characteristics.
Thus, there was caused a result of increasing the price of the air bag device, due to much labor in the folding operation and the cost of the parts to be added and the cost for attaching them.
One example of known air bag folding methods is disclosed in Japanese Patent Laid-open Publication 5-305852. The air bag device disclosed in the publication is equipped with a folded bag, an inflator for supplying gas into the bag, and a case for accommodating the bag and the inflator, and a hinged door on the opening side of the case. The folding steps of the bag include the steps of folding the bag flat so that exhaust holes on side portions of the bag are on imaginary folding lines; folding the bag in a rectangular form to have a width corresponding to the width of the opening portion of the case by folding back the both end portions of the bag folded flat; folding the bag zigzag toward the opening portion side in a manner to set as a tip an end peripheral portion of the bag that is opposite to the opening portion of the case; storing the entirety of the bag in the case in a condition in which the zigzag folded portion is positioned on an inner side and its periphery is surrounded.
In the above-mentioned folding steps, however, the bag is folded zigzag, and at last a roll folding is conducted to cover the zigzag folded bag portion. Such roll folded portion follows a rewinding process upon the deployment. Therefore, there is a tendency to have some deployment time. To suppress the tendency, for example, there is a method of increasing the output of the inflator. This, however, rapidly increases the inner pressure of the bag upon the start of the deployment. Thus, it may be necessary to provide the bag with a sufficient reinforced structure. Such reinforced structure makes the packing size of the bag larger, resulting in the increase of the cost. This causes a dilemma.